[Gllug] Public IPs - When are they appropriate

[Stephen Harker]

On Thursday 15 November 2001 08:41, you wrote:
> On Wed, 14 Nov 2001, tet at accucard.com stipulated:
> >>Not enough to give each living cell its own IP address.
> >>
> >>(Damn, there go *those* world domination plans...)
> >
> > Are you sure about that? I've seen estimates for the number of
> > living cells on earth at 10^30, while IPv6 provides 3.4 x 10^38
> > addresses...
>
> I was sure, but I'd made a stupid maths error. You're right, every
> cell has a good few IP addresses (so we have a good ten trillion
> plus per person).

I sent this to my brother (a geology/chemistry graduate) and he 
said...

"Re: IPv6
Date: Wed, 14 Nov 2001 17:06:52 +0000
From: Jonathan Harker <jharker at tridex.co.uk>
 To: Stephen Harker <steve at pauken.co.uk>

 Sad Linux geeks.

I'm afraid the Earth is 12756 km in diameter, not 10000 km, and it is 
not a 
sphere, but an equatorially oblate spheroid (surface topography 
notwithstanding).

The surface area of spheroids is

4 * pi * cuberoot(r1 ^ 2) * cuberoot(r2 ^ 2) * cuberoot(r3 ^ 2)

where r1, r2 and r3 are the perpendicular axial radii (x, y, z axes). 
In an 
equatorially oblate spheroid, r1 = r2, so you can simplify to

4 * pi * cuberoot(r1 ^ 4) * cuberoot(r2 ^ 2)

where r1 is the equatorial diameter and r2 is the polar diameter. 
Given a 
maximum polar oblateness of +/- 35 km, we can say the SA is roughly

4 * pi * cuberoot(12756000 ^ 4) * cuberoot(12721000 ^ 2) square metres

= 2.04 * 10^15 square metres

So given about 4 * 10^37 unique allocatable IPv6 addresses, there are 
about 
2 * 10^22 addresses per square metre, or 20 thousand per square 
nanometre. 
Visible light wavelengths are hundreds of nanometres!

If each IP address were a grain of sand, there would be enough to 
fill two 
million planet Earths (volume is about 8.7 * 10^21 cubic metres)."

So there you go. I'll thump him next time I see him.
-- 
Stephen Harker
steve at pauken.co.uk, http://www.pauken.co.uk
"Beep Beep" - R2D2

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